Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $217.84   4.553%   $227.7583   $227.76   $227.75   $227.80  
  Purchase #2 $133.82   11.719%   $149.5024   $149.50   $149.50   $149.50  
  Purchase #3 $192.96   10.475%   $213.1726   $213.17   $213.15   $213.20  
  Purchase #4 $54.31   5.326%   $57.2026   $57.20   $57.20   $57.20  
  Purchase #5 $48.26   5.551%   $50.9389   $50.94   $50.95   $50.90  
  Purchase #6 $206.89   12.644%   $233.0492   $233.05   $233.05   $233.00  
  Purchase #7 $128.83   12.585%   $145.0433   $145.04   $145.05   $145.00  
  7 purchase totals = $982.91       $1,076.6673   $1,076.66   $1,076.65   $1,076.60